Integrated Si photonics is seen as a promising emerging technology to meet the industry imperative to reduce energy dissipated/bit for data transfer. A common integrated technology for Si photonics uses Si waveguides, formed on deep BOX SOI (buried oxide in silicon on insulator technology) (2 um thick) and cladded or encapsulated with SiO2. A common device used with Si photonics is the micro-ring, which can be used for modulators, ADD/drop filters, and MUX/DEMUX, due to its compact size.
The micro-ring is a resonant device tuned to a particular wavelength, and is hence very sensitive to thermal effects (e.g., from nearby analog drive circuits of logic). For example, if the ring expands due to heating, it is no longer tuned to the desired wavelength. To reduce impacts of temperature changes, heaters are built into the integrated photonics stack under or over the micro-rings. For example, as Si shows a strong dependency of optical properties on temperature, heaters can be used to control component temperature.
However, the heaters have many drawbacks such as dissipation of power, which is in conflict with the imperative to reduce energy/bit for data transfer. Also, the heaters require significant additional energy, exhibit unidirectional heating only, and they are difficult to be applied for practical use in integrated photonic systems. In addition, forming the heaters requires additional process steps. Furthermore, control of the temperature requires additional active circuitry, which adds yet more processing steps and complexity in the Si photonics chips/substrate.